Process for the extraction of tungsten values from materials containing same



United States Patent Ofifice 3,047,361 Patented July 31, 1962 PROCESS FOR THE EXTRACTION F TUNG- STEN VALUES FROM MATERIALS CONTAIN- ING SAME Harold M. Hubbard, Green Acres, and John H. Kennedy,

Radnor Green, DeL, assignors to E. I. du Pont de Nemours and Company, Wilmington, Del, a corporation of Delaware No Drawing. Filed Sept. 11, 1961, Ser. No. 135,418 7 Claims. (Cl. 2319) The present invention relates to a process for the recovery of tungsten values from tungsten-containing ores and minerals. More particularly, the present invention relates to a technique for the recovery of tungsten values from ore leaches and concentrates which are prepared from crude tungsten-bearing ores and minerals.

This application is a continuation-impart of our copending application Serial No. 811,016, filed May 5, 1959, now abandoned.

Tungsten-bearing ores are generally classified in two principal groups: The wolframite group and the scheelite group. Scheelite itself is the only commercially significant member of the scheelite group of ores, though certain other minerals in this group are of some significance, viz., powellite, stalzite, raspite, wulfenite, chillagite, tungstenite, hollandite, etc. In the wolframite group, there are three minerals of substantial economic importance: wolframite itself, ferberite, and huebnerite. The wolframite group also includes a number of other minerals of somewhat lesser economic importance, viz., reinite, ferritungstite, limonite, hydrotungstite, etc. The process of the present invention is operative for the recovery of tungsten values from any of the ores and minerals of both the wol-framite and scheelite groups.

The conventional techniques for working up tungstenbearing ores usually involve the solubilization of the tungsten values in the form of a sodium or potassium tungstate which is then purified by a series of repeated crystallizations as ammonium para-tungstate or tungstic acid. This is usually done by digesting the ore concentrate obtained from such conventional dressing techniques as gravity concentration, floatation, magnetic separation, or the like under pressure with an aqueous alkaline solution, such as aqueous sodium carbonate, potassium carbonate, or sodium hydroxide. Sometimes the ore concentrate is simply fused with the solid alkaline reagent. While these and related recovery techniques have met with varying degrees of success in recovering tungsten from tungstenbearing ores and minerals, they are relatively cumbersome and costly.

It is an object of the present invention to provide a novel process for the recovery of tungsten values from tungsten-bearing ores and minerals. It is a further object of the invention to provide such a process which is safe, convenient, and economical to perform. Other and additional objects of the invention will become apparent from a consideration of the ensuing specification and claims.

Broadly stated, the process of our invention consists of several distinct steps, the first of which is a digestion of the ore concentrate with a strong mineral acid which consists at least in part of ortho-phosphoric acid to: dissolve the tungsten values in the ore concentrate via the formation of a soluble hereteropoly phosphotungstic acid comlex. The phosphotungstic acid complex is then separated from impurities which are also soluble in the acid medium by extraction therefrom with an oxygenated organic solvent. Finally, the phosphotungstic acid complex is broken down into separate tungstate and phosphate components by treatment of the organic solvent solution with an aqueous alkaline solution; the tungstate and phosphate components passing from the organic phase into the aqueous alkaline phase in which they are more soluble. The

tungsten values can be recovered from the aforementioned aqueous alkaline phase by conventional techniques described more fully hereinafter. However, in accordance with a preferred embodiment of this invention, the tungstate and phosphate values in the aqueous phase are thereafter separated by contact with a strong base anion exchange resin, for example, of the quaternary ammonium type, which will preferentially adsorb the tungstate values to a much greater extent than the phosphates. The small percentage of the latter taken up by the resin may be easily washed off with a dilute alkaline solution and the tungsten values held by the resin may be recovered by elution with a concentrated inorganic salt solution. If the aforementioned preferred anion exchange separation is employed, the tungsten values are then recovered from the aforementioned inorganic salt solution as a tungstic acid precipitate by any of a variety of conventional .techniques.

The invention will be further illustrated in the following discussion and specific examples. The crude tungstenbearing ore is first dressed by any of the conventional techniques, such as gravity concentration, floatation, mag netic separation, air-cabling, electrostatic separation, or the like. The tungsten values are then leached from the ore concentrate by digestion with a strong mineral acid composition which consists at least in part of ortho-phosphoric acid to convert the tungsten to a soluble heteropolyphosphotungstic acid complex. In many instances phosphoric acid alone is quite satisfactory provided that the concentration is maintained sufficiently high. In many cases, however, it will often be desirable to maintain the phosphoric acid concentration as low as possible in order to minimize subsequent problems in the ultimate phosphate-tungstate separation. Thus, the acid composition employed for the digestion will normally be a mixture of phosphoric acid with one or more other mineral acids, such as hydrochloric acid or sulfuric acid, the latter being preferred.

The precise acid composition selected in any instance will depend greatly upon the composition of the ore and the ore concentrate. For example, the optimum acid composition for digestion of a scheelite concentrate will be an acid mixture which is 3-9 molar in sulfuric acid and 0.31.0 molar in phosphoric acid. Alternatively, phosphoric acid alone may be used if the concentration employed is within the 7-12 molar range.

Ores of the wolframite group, on the other hand, require much more drastic acid conditions. Best yields were obtained in working up these ores where both the phosphoric acid and sulfuric acid concentrations were in the 48 molar range. Lower phosphoric acid concentrations are operable, e.g., 1.5 molar, if the sulfuric acid concentration is extremely high; and conversely, the use of large amounts of phosphoric acid permits a corresponding decrease in the sulfuric acid concentration.

The optimum amounts and relative proportions of the acid components present in the acid composition will vary somewhat from case to case, depending upon the nature of the ore concentrate, the amount of acid-consuming gangue in the ore concentrate, and the temperature conditions during digestion. In all cases, sufficient phosphoric acid must be present to convert all of the tungsten to the heteropoly phosphotungstic acid. The total amount of acid present should be such that, after the gangue material in the ore is neutralized, the pH of the mixture is still low enough to retain the heteropoly phosphotungstic acids in solution, i.e., a pH of about 2 or less.

Temperature has a substantial effect on the efficiency of the digestion; and, generally speaking, the ultimate tungsten yield increases with elevation of the temperature during the digestion step. We have found it especially convenient to operate in the vicinity of the boiling point spat/eel of the acid mix which, with the strong mineral acids here involved, will generally fall between 100-175 C. The digestion vessel can, of course, be pressurized to facilitate the achievement of higher temperatures. Temperatures in the neighborhood of about 80 C. represent a practical lower limit for the digestion since the process proceeds too slowly at lower temperatures to be of any commercial significance.

Digestion periods, on the other hand, are not generally critical. Optimum digestion periods will vary from case to case depending upon the composition of the feed material. For the work-up of most ores, digestion times in the vicinity of two hours are quite adequate, and yields are not appreciably increased :by extending the digestion period beyond this point. If the tungsten concentration in the ore is exceptionally low, an increase in digestion time may effect a corresponding increase in the ultimate yield of tungsten.

As a result of the phosphoric acid digestion, the tungsten values are converted to a soluble heteropoly phosphotungstic acid complex. The precise composition of this complex will vary somewhat from case to case depending upon the digestion conditions. The phosphotungstic acids formed are predominantly those represented by the empirical formulas H P W O and H PW O The formation of the former is favored by high phosphoric acid concentrations and long digestion periods while the formation of thelatter is favored by lower phosphoric acid concentrations. A number of other complex heretopoly acids of tungsten and phosphorus are also known in which the proportions of P O :WO vary from 1:24 down to 1:6. In many cases the heteropoly phosphotungstic acid formed during the digestion is doubtless a mixture of a number of these acid complexes. At any rate, the precise structural nature of the heteropoly acid(s) formed is not critical to the process of the present invention inasmuch as their behavior in the subsequent steps of the process does not differ materially according to their structure.

The digestion of a number of tungsten-bearing ores in both the wolframite and scheelite groups is illustrated by Examples 1 through 9 which follow.

Example 1 20.0 grams of a scheelite concentrate which contained 26.6% W0 was digested for three hours in a solution composed of 125 ml. of water and 75 ml. of 85 orthophosphoric acid. During this period, the mixture was stirred slowly and the temperature was maintained at the boiling point. The solution was filtered while hot, cooled, and its tungsten content determined. The tungsten found in the leach solution accounted for 103 15% of the tungsten in the concentrate.

Example 2 100 grams of a scheelite concentrate containing 26.6% W0 was digested for four hours at 105 C. in a mixture composed of ml. of 85% orthophosphoric acid, 75 ml. of 98% sulfuric acid and 200 ml. of water. After digestion the mixture was filtered. 121 .grams of insoluble residue was recovered and analyzed for tungsten. 93% of the tungsten had been solubilized. This figure was confirmed by analysis of the leach solution.

Example 3 100 grams of a high grade scheelite concentrate containing 68.5% W0 was digested for three hours in a mixture of 35 ml. of 85 of orthophosphoric acid, 100 ml. of 98% sulfuric acid, and 370 ml. of water. The temperature was maintained at the boiling point, 108 C., and the mixture was stirred vigorously throughout the digestion. Analysis of the leach solution after filtration showed that 98.5% of the tungsten in the ore had been dissolved.

Example 4 20.0 grams of a ferberite concentrate which analyzed 4 12.6% W0 was digested for three hours in a boiling mixture of 100 ml. of orthophosphoric acid and ml. of water. The solution was filtered and analyzed. 70% of the W0 originally present in the concentrate was found in the filtrate.

Example 5 100 grams of ferberite concentrate containing 12.6% W0 was digested for four hours at 150 C. in a mixture of 100 ml. of 98% sulfuric acid, ml. of 85 orthophosphoric acid and 25 ml. of water. The insoluble residue which weighed 90 grams was found to be 1.7% W0 Thus 88% of the W0 in the original concentrate was dissolved by the digestion process.

Example 6 25.0 grams of a ferberite concentrate containing 12.6 W0 was digested for two hours at 170 C. in a mixture of 100 ml. of 98% sulfuric acid, ml. of 85 orthophosphoric acid and 25 ml. of water. Analysis of the filtrate accounted for 100% of the W0 in the concentrate.

Example 7 20.0 grams of a huebnerite concentrate containing 14.7% W0 was digested for three hours in a boiling mixture of 100 ml. of 85% orthophosphoric acid and 100 ml. of water. Analysis of the filtrate showed that 24% of the W0 in the concentrate had been dissolved.

Example 8 20.0 grams of a huebnerite concentrate containing 14.7% W0 was digested for three hours in a boiling mixture of 50 ml. of 85 orthophosphoric acid, 50 ml. of 98% sulfuric acid, and 50 ml. of water. Analysis of the filtrate accounted for 52% of W0 in the concentrate.

Example 9 20.0 grams of limonite ore (0.95% W0 was digested for 19 hours in a hot solution consisting of 50 ml. of 85% orthophosphoric acid, 50ml. of 98% sulfuric acid and 100 ml. of water. Analysis of the filtrate showed that 96% of the tungsten originally contained in the ore was dissolved by the digestion process.

Following the phosphoric acid leach by which the tungsten values are converted to the heteropoly phosphotungstic acid complex, the latter is extracted from the acid leach solution by means of an organic solvent in which the heteropoly acid complex is soluble. Suitable organic solvents in this connection include the moderately polar and highly polar organic solvents, and within this category the oxygenated organic solvents are preferred. In this latter connection such organic solvents as alcohols, ketones, diketones, ethers, polyethers, carboxylic acid esters, phosphoric acid esters, and the like are especially suitable. Many of the nitrogen-containing polar solvents are also satisfactory, as for example, the cyano hydrocarbons such as benzonitrile.

Temperature has no substantial" effect on the efiiciency of the extraction. Acid concentration, however, can affect the extraction. Solutions containing a large excess of acid are best diluted prior to the extraction with organic solvent. For optimum results in the extraction step, the phosphoric acid concentration is preferably adjusted below about 1.5 molar and the sulfuric acid concentration between about 0.2 and 2 molar.

The amount of solvent preferably used in any instance is a function of the amount of tungsten in the acid leach solution. Generally speaking, the solvent will be employed in an amount of about 1 ml./ 10 -100 mg. of W0 in the feed. The organic solvent extraction of the heteropoly phosphotungstic acid complex in the acid leach solution is illustrated by Examples 10-17 which follow.

Example 10 A solution of phosphotungstic acid was prepared by digesting a sample of scheelite concentrate in a mixture of sulfuric and orthophosphoric acids. The filtrate from this digestion was diluted with water to give a feed solution of the following composition: 10.2 mg./ml. W 3.0 M H 80 0.2 M H PO4. 25.0 ml. of this feed solution was shaken for two minutes in a separatory funnel with an equal volume of dibutoxytetraethylene glycol. An analysis showed that the tungsten was extracted quantitatively into the organic solvent. The aqueous waste contained no detectable tungsten (i.e., less than 0.1 mg./ml.).

Example 11 The acid scheelite leach solution of Example 2 was diluted to give a solution containing 46.4 mg./ml. W0 with an acid concentration of 1.2 M H 80 and 0.5 M H PO 100 ml. of this solution was shaken for two minutes in a separatory funnel with 50' ml. of tri-nbutylphosphate. No tungsten was detected in the aqueous waste after extraction.

Example 12 The acid ferberite leach solution of Example was diluted with water to give an extraction feed of the following composition: 4.81 mg./ml. W0 0.8 M H SO 0.9 M H PO 100 ml. of this feed solution was shaken for three minutes with 50 ml. of tri-n-butylphosphate. The aqueous waste was drawn off, a second 100 ml. portion of feed solution was added to the separatory funnel, and the extraction repeated. This process was continued until a total of 500 ml. of feed solution had been extracted. The aqueous Wastes from each extraction were combined to give a solution, Whose volume was 480 ml. and whose W0 content was 0.02 mg/ml. Therefore, 96% of the tungsten in the feed was extracted into the organic solvent.

Example 13 The acid ferberite leach solution of Example 8 was adjusted to give an extraction feed of the following composition: 1.03 rug/ml. W0 1.9 M H 80 1.0 M H PO 75 ml. of this feed was shaken for two minutes in a separatory funnel with 25 ml. of dibutoxytetraethylene glycol. Analysis of the aqueous waste showed that 61% of the tungsten in the feed was extracted by the organic solvent.

Example 14 25 ml. of a synthetic feed solution containing 34.6 mg./ ml. W0 0.9 M H 50 and 0.14 M H PO was shaken for three minutes in a separatory funnel with an equal volume of methylisobutyl ketone. Analysis of the aqueous waste showed that 96% of the tungsten was extracted by the solvent.

Example 15 50 ml. of n-butyl alcohol was placed in a separatory funnel. 50 ml. of a feed solution (42.5 mg./ml. W0 0.9 M H 80 0.15 M H PO was added and the mixture was shaken for five minutes. Analysis of the aqueous waste showed that 98% of the tungsten was extracted by the solvent.

Example 16 50 ml. of the feed solution of Example 15 was contacted with an equal volume of acetyl acetone. Analysis of the aqueous waste showed that 73% of the tungsten was extracted by the solvent.

Example 17 50 ml. of the feed solution of Example 15 was contacted with an equal volume of n-amyl acetate. Analysis of the aqueous waste showed that 20% of the tungsten was extracted by the solvent.

According to the present invention, recovery of the tungsten from the organic solvent solution of the heteropoly phosphotungstic acid depends upon the fact that such acids decompose in alkaline solution and that the phospate and tungstate decomposition products which result are substantially more soluble in Water than they are in the organic solvent. The organic solvent solution of the heteropoly acid is, therefore, back-stripped, i.e., contacted with an aqueous solution of a base, such as, for example, sodium hydroxide, potassium hydroxide, sodium bicarbonate, ammonium hydroxide, or a mixture thereof. Upon contact of the organic solvent solution with the aqueous base, the heteropoly acid complex breaks down into phosphate and tungstate components which will preferentially pass into the aqueous phase. The base is used in an amount at least sufiicient to neutralize all of the heteropoly acid in the solvent. The phosphate and tungstate decomposition products of the heteropoly phosphotungstic acid complex are largely simple normal and/or polytungstates (depending upon pH) and orthophosphate compounds. Normal tungstates tend to form at higher pH values.

The ease with which the tungsten can be recovered by back-stripping the organic solvent solution of the phosphotungstic acid varies from case to case depending upon the specific solvent system, the precise nature of the heteropoly phosphotungstic acid complex, and to some extent the temperature. In this latter connection, increased temperature, as noted below, facilitates the back-stripping. Generally speaking, the W18 phosphotungstic acid referred to above is easier to recover from the organic phase than the W composition since the latter is highly solvated by the solvent.

Though temperature is not generally critical to this step, the tungsten recovery is enhanced by operating at somewhat elevated temperatures, for example, 90 C. Contact time of the organic solvent solution and the agueous base will vary with the conditions on a case-tocase basis. Thirty minutes is usually satisfactory to give good recovery of the tungsten from the organic solvent, as is illustrated by Examples 18-24 which follow.

Example 18 The organic product from Example 10, a solution of phosphotungstic acid in dibutoxytetraethylene glycol, was shaken for five minutes in a separatory funnel with an equal volume of 5 normal sodium hydroxide. The aqueous layer was drawn off and analyzed. It contained 0.2122 gram of W0 representing recovery of 84% of the tungsten from the organic solvent.

Example 19 A solution of phosphotungstic acid in tri-n-butyl phosphate was prepared by extracting a scheelite leach solution as described in Example 10. The pregnant organic solvent was back-stripped by shaking it for five minutes in a separatory funnel with 2 normal sodium hydroxide. The aqueous product was drawn 01f. Then an additional portion of scheelite leach solution was extracted by the solvent. The solvent was stripped a second time with fresh 2 normal sodium hydroxide. This procedure was repeated through four complete cycles. The four sodium hydroxide product solutions were combined and analyzed. They contained 18% of the W0 originally present in the leach. Then the organic solvent was shaken for 10 minutes with an equal volume of '3 normal ammonium hydroxide. The ammonia product was drawn off, analyzed, and found to contain 53% of the tungsten originally present in the leach solution.

Example 20 The pregnant tributylphosphate solution from the extraction of a ferberite leach solution of Example 12 was stripped in a separatory funnel with an equal volume of 2 normal sodium hydroxide. The aqueous product was drawn off and found to contain 1.05 grams of W0 This represented a tungsten yield of approximately 60%. The organic phase was contacted successively with two more portions of 2 normal sodium hydroxide, but no additional tungsten was recovered. Then the organic solvent was placed in a round bottomed flask with an equal volume of 2 normal sodium hydroxide. The flask was heated on the water bath to 90 C. and stirred vigorously for 30 minutes. The aqueous product was removed and found to contain 0.43 gram of W Examination of the organic phase by emission spectroscopy showed its tungsten content to be less than 100 p.p.m.

Example 21 The pregnant organic solution from the extraction of huebneri-te leach of Example 13 was shaken for five minutes in a separatory funnel with an equal volume of normal sodium hydroxide. 90% of the tungsten in the organic solution was recovered in the aqueous product.

Example 22 The solution of phosphotungstic acid in methylisobutyl ketone of Example 14 was contacted with two successive portions of 1 normal sodium hydroxide. In each case the organic solvent was shaken for three minutes in a separatory funnel with an equal volume of stripping agent. 90% of the tungsten originally present in the solvent was recovered in this proces; 54% in the first aqueous product and 43% in the second.

Example 23 20 ml. of a solution of phosphotungstic acid in dibutoxytetraethylene glycol which contained a total of 0.3675 gram of W0 was shaken for minutes in a separatory funnel with an equal volume of 1 molar sodium carbonate. The aqueous product contained 0.1919 gram of W0 representing a 52% recovery.

Example 24 20 m1. of a solution of phosphotungstic acid in dibutoxytetraethylene glycol was placed in a flask with an equal volume of 5 normal potassium hydroxide. The flask was warmed to 60 C. and its contents were stirred vigorously for five minutes. The organic solution originally contained 0.3675 gram of W0 After the extraction, 0.281 gram of W0 77% of the original amount, was found in the aqueous product.

As indicated hereinbefore separation of the phosphate and tungstate components in the aqueous phase canv be accomplished either by any of the conventional techniques for separating phosphate from tungstate components or, preferably, in accordance With one unique embodiment of this invention, by means of a strong base anion exchange resin.

The anion exchange resin employed in accordance with the aforementioned preferred process normally, although not necessarily, will be of the quaternary am monium type. A typical resin of this type is represented by the structure:

Resins of this type are readily available on the commercial market as Dowex 1 and Dowex 2 (Dow Chemical Co.), Amberlite 400 (Rohm and Haas 00-), Perrnutit S-1 and Permutit FF (Permutit Co.). Further details of the structure and operation of these ion exchange resins may be found in Kunin, Ion Exchange Resins, John Wiley and Sons, Inc., N.Y., NY. (1958), Second Edition, pp. 80 and 89.

We have found that the strong base anion exchange resins will much more strongly adsorb the tungstate than the phosphate from an alkaline solution. The strong base anion exchange resin will take up essentially all of the tungstate while showing much less aflinity for the phosphate. The small amount of phosphate which the resin does pick up is easily removed by Washing with a dilute alkaline solution and the tungsten compounds are thereafter recovered substantially free of phosphorus by elution with a relatively concentrated inorganic salt solution, such as sodium chloride, sodium nitrate, sodium sulfate, the cognate potassium and ammonium salts, and the like, etc.

Good results have been obtained with an eluting agent having a concentration of 2-4 molar, though other concentrations are also operable.

In the case of anion exchange resins of the quaternary ammonium type (which are preferred), it will often be desirable to convert the resin from the chloride form in which it is stored to the hydroxide form prior to the tungstate-phosphate separation since the (OH) ion is more easily replaced by the tungstate than (Cl). This may be done by pretreating the column of the resin with four to eight column volumes of sodium hydroxide solu tion.

The basicity of the column feed may vary over a relatively wide range, from neutrality up to a hydroxide concentration of approximately 4 normal, though hydroxide concentrations of 0.1 to 1.5 normal are generally preferred. The concentration of tungsten and phosphate in the feed solution is not generally critical to the separation with the resin. Especially good results have been obtained with tungsten concentrations in the column feed of from 10-100 mg. W0 per ml. The WO /P O weight ratio may likewise vary widely and ratios of 0.5-/1 have proven quite satisfactory.

Examples of conventional procedures which can be employed for the tungstate-phosphate separation instead of the unique anion exchange resin separation just described are, for example, fractional precipitation of the phosphate, for example, as magnesium ammonium phosphate, or fractional precipitation of the tungstate, for example, with such organic compounds as chinchonine or S-hydroxyquinoline. The magnesium ammonium phosphate separation involves treating the aqueous phase obtained as described hereinbefore with magnesia reagent, preferably at low temperature to precipitate magnesium ammonium phosphate which is then filtered off, preferably at low temperature, to yield a tungstate solution comparable to that obtained in the anion exchange resin separation. Preferably, the solution to be treated is weakly basic. Undue excess of base is preferably avoided. The chinchonine and 8-hydroxyquino1ine separation involve adding the aforementioned compounds to the aqueous phase to precipitate the tungstate. Tungsten values can be recovered from the resulting precipitate by ignition at temperatures on the order of 600 to 800 C. In the chinchonine separation, the chinchonine is preferably added to the aqueous phase along with strong mineral acid to yield a precipitation media about 1 to 3 molar with respect to the acid. Standing in warm solution also aids in coagulation and precipitation, although such standing is not essential.

The tungstate-phosphate separation by means of the preferred anion exchange resin method 'is illustrated in Examples 2528.

Example 25 A small glass column was filled with 50 ml of air-dried Amberlite IRA-400, a strong base, anion exchange resin of the quaternary ammonium type in the chloride form manufactured by the Rohm and Haas C0. The depth of the resin bed in the column was 250 mm. The diameter was 18 mm. and the free column volume was 23 ml. The product produced by ammonia stripping in Example 19 was used as feed for this column. The solution contained 76 mg./ml. W0 5 mg./ml. P 0 and was approximately 3 normal with respect to ammonium hydroxide. The feed was run through the column, and the column was washed with ml. 0.5 normal sodium hydroxide to remove the phosphate. Finally the tungsten was recovered by elution with a 4 normal sodium chloride solution. Throughout the entire process the flow rate of liquid through the column was maintained at 5 ml. per minute. All of the phosphate was recovered in the first 75 ml. of 0.5 normal sodium hydroxide wash. 95% of the tungsten was found in the first 75 ml. of sodium chloride solution. No phosphorus could be detected in the tungsten solution.

Example 26 The extraction product described in Example 20 and the products of two more similar extractions were combined to give a solution containing 7.4 rug/ml. W and 8 mg./ml. P 0 This solution was approximately 2 normal with respect to sodium hydroxide. 120 ml. of this feed solution was fed to the ion exchange column described in Example 25. In this case, however, the resin was converted to the hydroxide form with aqueous sodium hydroxide before the introduction of the feed. After the feed had passed through, the column was washed with 200 ml. of 0.5 normal sodium hydroxide, and then tungsten was eluted with 4 .normal sodium chloride. All of the phosphate appeared in the first 175 ml. of solution taken from the bottom of the column. 94% of the tungsten was recovered in the first 50 ml. of sodium chloride solution put through the column. Spectroscopic examination of the tungsten product showed a phosphorus content of 15 to 75 p.p.m.

Example 27 A column feed was made up having the following composition: 27.7 mg. WO /ml., 8.6 mg. P O /ml., 1.0 N NaOI-I. The resin in the ion exchange column of Example 25 was converted to the hydroxide form by passing 250 ml. of 2 normal sodium hydroxide through it and this was followed by a distilled Water wash. 200 m1. of the feed solution was run through the column at a rate of 12 ml./minute. This was followed by 50 ml. of distilled water to wash out the column and then tungsten was eluted with 4 normal sodium chloride solution. 90% of the tungsten was recovered in the first 75 ml. of sodium chloride. The phosphate content of the tungsten product was deter mined chemically and found to be less than 0.3 mg./m1.

Example 28 Samples of Amberlite IRA-400 resin which had been complexed with tuugstate (23.5% W0 were equilibrated on a mechanical shaker with salt solutions for 24 hours. At the end of that time the amount of tungsten leached from the resin by the salt solution was determined, as set forth in the following table:

The following examples illustrate conventional methods which can be employed for the phosphate-tungstate separation.

Example 29 To 400 ml. of an aqueous phase obtained by the general procedures of Examples 18 to 24 containing 27.7 mg./ml. W0 8.6 mg/ml. P 0 and 3 molar with respect to potassium hydroxide is added 300 ml. of 6 M hydrochloric acid and 600 ml. of magnesia reagent. After the magnesium mixture and hydrochloric acid are added to the aqueous phase, the resulting mixture is neutralized with concentrated ammonium hydroxide and 20 ml. excess ammonium hydroxide is added thereto. The mixture is cooled in ice for two hours and magnesium ammonium phosphate filtered therefrom. Preferably, the magnesium ammonium phosphate precipitate is redissolved in dilute hydrochloric acid and a second precipitation is performed. However, the product of the first precipitation after ignition weighs 2.7 grams and contains less than 2% tungsten. The filtrate contains less than 0.1 mg./ml. of P 0 Tungsten can be precipitated from the resulting filtrate as tungsten trioxide in the usual manner by addition of a hydrochloric acid as indicated in Example 34.

The magnesia reagent employed above is prepared by dissolving 400 g. of magnesium chloride (hexahydrate) and 300 g. of ammonium chloride, in 1500 m1. of warm water. The solution is neutralized with ammonium hydroxide, filtered, and then made slightly acidic with hydrochloric acid.

Example 30 To 200 m1. of a substantially neutral aqueous solution produced by ammonia stripping as described in Example 19 and containing 76 mg./ml. of W0 and 5 mg/ml. of P 0 are added 20 ml. of 6 M sodium hydroxide, then the resulting mixture is warmed to 60 C. Next, a mixture of 60 ml. of concentrated hydrochloric acid and 50 ml. of chinchonine solution are added thereto. The resulting precipitate containing the tungsten is filtered after standing for two hours. Ignition of the precipitate at 750 C. yields 15.0 g. of tungsten trioxide containing only a trace of phosphorus.

The chinchonine solution employed above is prepared by dissolving 100 g. of chinchonine in 760 of water and 100 ml. of concentrated hydrochloric acid.

Example 31 To a neutral or slightly alkaline phosphate-tungstate solution obtained by the general procedures described in Examples 18 to 24 is added an excess of a 4% solution of S-hydroxyquinoline in ethanol. The mixture is heated to boiling and acetic acid is added until the mixture is slightly acidic. The mixture is then heated to boiling and filtered. The resulting precipitate is washed with hot water and then ignited at 750 C. to yield tungsten trioxide.

The followirng example illustrates the process of the present invention starting with the ore digestion and carrying completely through the tungsten recovery:

Example 32 A scheelite concentrate (100 g.) containing 26.6% by weight W0 was digested at 105 C. for four hours in a sulfuric acid-phosphoric acid mixture, 4.7 molar in H 80 and 0.52 molar in H PO prepared by combining 75 ml. of 98% sulfuric acid, 10 ml. of orthophosphoric acid and 200 ml. of distilled water. The digested mixture was filtered and washed. The filtrate and washings were combined and diluted with distilled water to give one liter of a feed solution of the following composition: 25.76 mg./m'l. of W0 as phosphotungstic acids, 0.8 M H 50 0.06 M H PO (Digestion recovery, 97%.)

A 200 ml. aliquot of the feed solution was then shaken for three minutes in a separatory funnel with 100 ml. of tri-N-butyl phosphate, and the phases were separated. The aqueous phase contained only 200 p.p.m. tungsten and was discarded. The pregnant organic phase was stirred at C. with an equal volume of aqueous 2 normal sodium hydroxide for thirty minutes. Upon standing, the mixture separated into two layers. The aqueous layer contained the equivalent of 48.2 mg./ml. of tungsten trioxide, as tungstate. About 2000 p.p.m. of tungsten remained in the organic waste which was discarded. (Extraction and stripping yield, 96%.)

"Fifty milliliters of the aqueous product solution were fed into an ion exchange column substantially the same as that described in Example 25. The column was then washed with 250 ml. of 0.5 normal sodium hydroxide to remove the phosphate. The tungsten values were recovered by elution with 400 m1. of a 4 M sodium chloride solution. The eluate was collected in 25 ml. portions, and Sgml. portions were withdrawn for analysis. The three Ore Product Concentrate Ca .pereent 630% not detected W d *25% Major S1 ..d0 0.63.0% 0.02 0.1% Fe" 0--.. 0.42.0% 0.020.1% P d0 0.ll.0% 0.020.1% Mg d0 0.10.5% 0.010.05% AI p.p.m.. BOO-4,000 3001,500 Mn. p.p.m. 6003,000 20-100 Ti p.p.m 60-300 not detected Mo p.p.m 5025() 2,000 On p.p.1n -50 Trace The elution product from the anion exchange resin is a relatively pune solution of sodium tungstate in the aqueous salt. This product may be converted into tungstic acid by any of several conventional methods. Examples 33 and 34 are illustrative of two such techniques.

Example 33 To recover tungstic acid from the product of the phosphate-tungstate separation of Example 25, 50 ml. of this product (W0 content 28 mg./ml.) was heated to boiling and added to a hot solution of 1:4 hydrochloric acid. A precipitate of tungstic acid was collected on filter paper, ignited to W0 and analyzed. 1.35 grams of W0 97i5% of the tungsten in the product, was recovered. Analysis of this product is given below.

Phosphorous Not detected, 50 p.p.m. Arsenic Not detected, (100 p.p.m. Molybdenum 0.080.5%. Iron 100500 p.p.m. Silicon 0.080.5%. Sodium 0.11.0%. Calcium 50250 p.p.m. Tungsten trioxide 97% Example 34 To recover tungstic acid from the product of the phosphate-tungstate separation discussed in Example 27, a 10 ml. sample of this product was added to a boiling solution of 1:1 hydrochloric acid. 78% of the tungsten was precipitated as tungstic acid. Phosphorus could not be detected in the precipitated acid by emission spectroscopy.

The process of the present invention comprising conversion of tungsten values to a soluble heteropoly phosphotungstic acid complex, separation of the complex with a polar organic solvent, and decomposition of the complex to yield an aqueous solution of tungsten values free of ore and mineral impurities as described herein represents a new approach to the beneficiation of tungsten-bearing ores and minerals. The conversion of tungsten values in such materials to a soluble heteropoly phosphotungstic acid complex and treatment of the complex as described herein coupled with the ultimate separation of the phosphate and tungstate components of this complex by means of an anion exchange resin represents a distinctly new and preferred technique in the recovery of tungsten from its natural ores and the like. The process of this invention offers a number of important advantages compared to the conventional techniques commonly used. The digestion temperatures employed (100175 C. at atmospheric pressure) are significantly lower than those required for fusion of the ore with a solid alkaline reagent (-900 C.),

and are even lower than those customarily employed for digestion of the ore with an alkaline reagent (-200 C. at a pressure of about 200 p.s.i.). The acid decomposition techniques, on the other hand, usually require an oxidizing agent in combination with the acid. Another advantageous feature of the present invention is that the process is highly selective and results in a product of high purity. This eliminates the necessity for repeated precipitations and recrystallizations. Also, the process of the present invention is effective with all types of ores, including very low-grade ores, and makes possible the extraction of tungsten from low-grade tungsten-bearing ores which would not be otherwise economically feasible.

The invention has been described in detail in the foregoing specification. It will be readily apparent tothose siklled in the art that many variations may be made in the techniques and compositions described without departing from the spirit or scope of the invention. 'It is intended, therefore, to be limited only by the following claims.

We claim:

1. A process for the extraction of tungsten values from tungsten-bearing ores, minerals, ore leaches, ore concentrates and the like which comprises heating the tungstencontaining material to a temperature between 80 C. and the boiling point of the mass with a strong mineral acid composition which consists of at least in part of orthophosphoric acid to form a heteropoly phosphotungstic acid complex, said acid composition being present in an amount such that the pH of the resultant acidic mass is not greater than about 2, separating the phosphotungstic acid complex from the acidic reaction mass by extraction with an oxygenated polar organic solvent which preferentially takes up the phosphotungstic acid complex and decomposing said phosphotungstic acid complex into separate tungstate and phosphate components by contacting the organic solution of the phosphotungstic acid complex with an aqueous alkaline solution having sufficient base capacity to raise the pH of the mass to above about 7, said tungstate and phosphate components passing into the aqueous phase.

2. A process for the extraction of tungsten values from tungsten-bearing ores, minerals, ore leaches, ore concentrates and the like which comprises heating the tungstencontaining material to a temperature between 80 C. and the boiling point of the mass with a strong mineral acid composition which consists at least in part of ortho-phosphoric acid to form a heteropoly phosphotunstic acid complex, said acid composition being present in an amount such that the pH of the resultant acidic mass is not greater than about 2, separating the phosphotungstic acid complex from the acidic reaction mass by extraction with an oxygenated polar organic solvent which preferentially takes up the phosphotungstic acid complex, decomposing said phosphotungstic acid complex into separate tungstate and phosphate components by contacting the organic solution of the phosphotungstic acid complex with an aqueous alkaline solution having sufficient base capacity to raise the pH of the mass to above about 7, said tungstate and phosphate components passing into the aqueous phase, thereafter separating the tungstate and phosphate components by contacting said aqueous alkaline phase with a strong base anion exchange resin which will preferentially adsorb the tungstate component and recovering said tungstate component from said anion exchange resin by elution with a concentrated inorganic salt solution which will displace said tungstate component.

3. A process for the extraction of tungsten values from tungsten-bearing ores, minerals, ore leaches, ore concentrates and the like which comprises heating the tungstencontaining material to a temperature between 80 C. and the boiling point of the mass with an acid composition consisting of orthophosphoric acid to form a heteropoly phosphotungstic acid complex, said acid composition being present in an amount such that the pH of the resultant acidic mass is not greater than about 2, separating the phosphotungstic acid complex from the acidic reaction mass by extraction with an oxygenated polar organic solvent which preferentially takes up the phosphotungstic acid complex, decomposing said phosphotungstic acid complex into separate tungstate and phosphate components by contacting the organic solution of the phosphotungstic acid complex with an aqueous alkaline solution having sufficient base capacity to raise the pH of the mass to above about 7, said tungstate and phosphate components passing into the aqueous phase, thereafter separating the tungstate and phosphate components by contacting said aqueous alkaline phase with a strong base anion exchange resin Which will preferentially adsorb the tungstate component and recovering said tungstate component from said anion exchange resin by elution with a concentrated inorganic salt solution which will displace said tungstate component.

4. A process as in claim 3 wherein the anion exchange resin is of the quaternary ammonium type.

5. A process for the extraction of tungsten values from tungsten-bearing ores, minerals, ore leaches, ore concentrates and the like which comprises heating the tungstencontaining material to a temperature between 80 C. and the boiling point of the mass with an acid composition comprising a mixture of orthophosphoric and sulfuric acids to form a heteropoly phosphotungstic acid complex,

said acid composition being present in an amount such that the pH of the resultant acidic mass is not greater than about 2, separating the phosphotungstic acid complex from the acidic reaction mass by extraction with an oxygenated polar organic solvent, decomposing the phosphotungstic acid complex into separate tungstate and phosphate components by contacting the organic solution of the phosphotungstic acid complex with an aqueous alkaline solution having sufficient base capacity to raise the pH of the mass to above about 7, said tungstate and phosphate components passing into the aqueous phase, thereafter separating the tungstate and phosphate components by contacting said aqueous alkaline phase with a strong base anion exchange resin which will Preferentially adsorb the tungstate component and recovering said tungstate component from said anion exchange resin by elution with aconcentrated inorganic salt solution which will displace said tungstate component.

6. A process as in claim 5 wherein the anion exchange resin is of the quaternary ammonium type.

7. A process as in claim 6 wherein said anion exchange resin is eluted with a concentrated sodium chloride solution.

No references cited. 

1. A PROCESS FOR THE EXTRACTION OF TUNGSTEN VALUES FROM TUNGSTEN-BEARING ORES, MINERALS, ORE LEACHES, ORE CONCENTRATES AND THE LIKE WHICH COMPRISES HEATING THE TUNGSTENCONTAINING MATERIAL TO A TEMPERATURE BETWEEN 80*C. AND THE BOILING POINT OF THE MASS WITH A STRONG MINERAL ACID COMPOSITION WHICH CONSISTS OF AT LEAST IN PART OF ORTHOPHOSPHORIC ACID TO FORM A HETEROPOLY PHOSPHOTUNGSTIC ACID COMPLEX, SAID ACID COMPOSITION BEING PRESENT IN AN AMOUNT SUCH THAT THE PH OF THE RESULTANT ACIDIC MASS IS NOT GREATER THAN ABOUT 2, SEPARATING THE PHOSPHOTUNGSTIC ACID COMPLEX FROM THE ACIDIC REACTION MASS BY EXTRACTION WITH AN OXYGENATED POLAR ORGANIC SOLVENT WHICH PREFERENTIALLY TAKES UP THE PHOSPHOTUNGSTIC ACID COMPLEX AND DECOMPOSING SAID PHOSPHOTUNGSTIC ACID COMPLEX INTO SEPARATE TUNGSTATE AND PHOSPHATE COMPONENTS BY CONTACTING THE ORGANIC SOLUTION OF THE PHOSPHOTUNGSTIC ACID COMPLEX WITH AN AQUEOUS ALKALINE SOLUTION HAVING SUFFICIENT BASE CAPACITY TO RAISE THE PH OF THE MASS TO ABOVE ABOUT 7, SAID TUNGSTATE AND PHOSPHATE COMPONENTS PASSING INTO THE AQUEOUS PHASE. 